Sensors of small, airborne particles such as dust typically incorporate a mechanical, electrical, or optical sensing mechanism from which a output, or response signal, is measured. The magnitude of this response signal is proportional to the dust quantity. Physical qualities of such dust, such as size, density, and concentration are determined from the effect on this output signal.
Known methods used to effect such a dust sensing system include optical sensors, such as that disclosed in U.S. Pat. No. 5,136,750 in which the flux received is clouded by intervening particulate matter, and mirror based systems, such as that disclosed by U.S. Pat. No. 5,412,221 which receive light reflected from a mirror onto which particles have accumulated. Other methods include mechanical and electronic stimulation of a sensing member, typically an electrostrictive or piezoelectric member, in which particulate accumulation affects the mass of the sensor.
Such devices are disclosed in U.S. Pat. No. 3,653,253, which suggests sampling the mass of an accumulating piezoelectric crystal at two successive points to approximate the particulate mass collected, and U.S. Pat. No. 3,715,911, which discloses coating a sensory member with a tacky substance to accumulate airborne particles.
Often such devices are prone to high maintenance, as cumulative particle accumulation minimizes the sensitivity, therefore mandating frequent cleaning and/or calibration to effect accurate readings. Such devices are also expensive to manufacture, requiring specialized optical or electronic components such as piezoelectric crystals, photoresistors, and photosensors. Additionally, such devices tend to require large amounts of, or precisely metered, electrical power, limiting effectiveness with regard to household AC or common battery power. Further, point based sensors such as piezoelectric crystals have a small sensitivity area, limiting effectiveness and requiring a plurality of sensors when applied to an area. It would be beneficial to utilize a sensor capable of being manufactured from a planar material in which the electronic sensing properties are uniform along the area of the sensor.